A Genetic Switch in Bacteriophages within the Peduovirinae Subfamily : Structure, Function and Evolution

The temperate bacteriophages in the Peduovirinae subfamily can either grow lytically or integrate into their bacterial host and form lysogeny. Which one of the two life cycles the phage will enter after infection is controlled by a transcriptional switch. The switch also controls the induction of genes necessary for an integrated phage, a prophage, to excise out of the host genome and propagate lytically. In its most simple form, the transcriptional switch consists of two proteins repressing each other’s promoters, which are oriented face to face in close proximity. The Peduovirinae phages contain two types of transcriptional switches. They were studied with phylogenetic methods to determine their evolution and distribution. Bioinformatic analyses showed that there were several new E. coli integration sites and new inferred immunity classes among the Peduovirinae phages. The two switch types fell into two distinct groups, with no overlap in any of the proteins, but these groups were not defined by host barriers. But in vivo distribution did show a host preference. The P2 C protein was crystallized and its 3D structure determined. It forms a symmetrical dimer in vitro, with an unstructured C-terminal end. The DNA binding domain was determined to lie in alpha helix three and narrowed down to three residues. The C terminal end of the protein is suggested to be part of tetramerization, but a nine amino acid truncation does not affect activity in vitro. In an attempt to discover the mechanism between the switch from lysogeny to lysis in phage P2 the interactions between the two switch proteins and the proteins of its host E. coli was analyzed. Eight E. coli proteins interacted with protein C or Cox, but no interaction between the two switch proteins was detected. Two E. coli proteins showed a distinct effect on the expression of C, and several affected the level of phage lysis. The mechanisms behind these effects are still unclear.At the time of the doctoral defence the following paper was unpublished and had a status as follows: Paper nr 3:Manuscrip